Rotary mower blade

ABSTRACT

A rotary mower blade is formed with a notch at each end of the blade. Upwardly inclined vanes are provided on trailing edges of end portions of the blade adjacent the respective notches. Intermediate a central portion of the blade and the end portions, surfaces are formed extending downwardly from the leading to the trailing edges of the blade.

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/317,184, filed Sep. 6, 2001.

BACKGROUND OF THE INVENTION

[0002] 1. Field Of the Invention

[0003] The present invention relates to a blade for a rotary mower, theblade being formed so as to reduce noise generated during moweroperation.

[0004] 2. Prior Art

[0005] The problem of noise generated by rotary mower blades has beenrecognized, and blades previously have been designed to reduce suchnoise. An example of such a blade is disclosed in European PatentApplication 0 300 642 A1, published on Jan. 25, 1989. This Applicationdiscloses a mower blade wherein each end portion of the blade issharpened at its leading edge for cutting purposes, and wherein at itstrailing edge, an upwardly extending vane is provided. The vanes aredisplaced inwardly from the outermost edges of their respective endportions.

SUMMARY OF THE INVENTION

[0006] The present invention represents an improvement over the mowerblade disclosed in European Patent Application 0 300 642 A1. Moreparticularly, the trailing edge of each end portion of the blade isprovided with a notch. The edge of each notch extends in a directionsubstantially perpendicular to the longitudinal axis of the blade for adistance approximating half of the blade's width. The notch edge thenchanges direction extending outwardly at an angle to the blade'slongitudinal axis until the notch edge reaches the outer edge of theblade. The trailing edges of the blade's end portions adjacent thenotches are bent upwardly, substantially along lines coextensive withthe direction of the respective notch edges as the latter extendoutwardly to the blade ends, to form an upwardly extending vane at eachend of the blade adjacent a notch. A central portion of the blade isjoined to the end portions by respective intermediate blade portionswhich are twisted relative to the blade's longitudinal axis so as toform inclined surfaces which descend from the leading edges of the bladeto the trailing edges.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The invention will be described in greater detail with respect tothe accompanying drawings, wherein:

[0008]FIG. 1 is a top plan view of a mower blade according to theinvention;

[0009]FIG. 2 is a side elevational view thereof;

[0010]FIG. 3 is a cross-sectional view thereof taken along line 3—3 inFIG. 1;

[0011]FIG. 4 is a cross-sectional view thereof taken along line 4—4 inFIG. 1; and

[0012]FIG. 5 is a perspective view of a portion of the blade shown inFIGS. 1 and 2.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

[0013] Referring to FIGS. 1, 2 and 5 of the drawings, a blade 10 isformed from a piece of flat bar stock of rectangular cross-section. Theblade includes a central portion 12 provided with an aperture 14 forreceiving the drive shaft of a rotary mower (not shown) to which theblade may be attached in a conventional manner. The central portion 12also includes upwardly bent edges 16 and 18 (FIG. 3).

[0014] The blade is further provided with end portions 20 and 22 joinedof the central portion 12 by intermediate portions 24 and 26,respectively. The intermediate portions 24 and 26 are twisted about thelongitudinal axis of the blade where they come together with centralportion 12 and with end portions 20 and 22, respectively. Moreparticularly, as viewed along the blade's longitudinal axis from endportion 22, the blade is twisted in a clockwise direction where centralportion 12 and intermediate portion 26 meet. Where intermediate portion26 joins end portion 22, the blade is twisted counterclockwise a likeamount. The result is that intermediate portion 26 forms an inclinedsurface (shown in cross-section in FIG. 4) which slopes downwardly fromthe leading edge of portion 26, at an angle of approximately 13°relative to the section of central portion 12 between edges 16 and 18.Where intermediate portion 24 meets central portion 12 and the endportion 20, the blade is twisted to the same degree, but in an oppositesense, to the way the blade is twisted with respect to intermediateportion 26. Thus, portion 24 also is formed with an inclined surfacewhich slopes downwardly, at an angle of approximately 13°, relative tothe section of central portion 12 between edges 16 and 18.

[0015] The trailing edges of the blade are formed with notches 32 and 34at opposite ends of the blade. Each notch is defined by an edgeextending substantially perpendicular to the longitudinal axis of theblade from a trailing edge of respective end portions 20 and 22 to alocation approximately midway between the leading and trailing edges ofthe blade. At that point, the notch edge changes direction to extendoutwardly, at an angle of approximately 30° relative to the longitudinalaxis of the blade, to the end of the blade. The corners formed by thechanges in direction of the notch edges are identified as 36 and 38.

[0016] The trailing edges of end portions 20 and 22 adjacent notches 32and 34, respectively, are bent to form upwardly extending vanes 40 and42, the bending occurring along lines substantially coextensive withthose portions of the notch edges extending from corners 36 and 38 tothe ends of the blade. The vanes 40 and 42 are bent approximately 30°with respect to the plane of adjacent segments of end portions 20 and22.

[0017] When a blade formed as just described is rotated by the engine ofa rotary mower, cutting edges 28 and 30 along the leading edges of theblade cut grass efficiently with reduced noise. As the blade rotates,the surfaces of intermediate portions 24 and 26, which slope downwardlyfrom the leading to trailing edges of portions 24 and 26, pressurize theair in the grass bed by forcing air into it. Pressure relief occursoutwardly of portions 24 and 26 due to centrifugal force. This pressurerelief causes air turbulence in the grass bed which results in the grassmoving upwardly into the path of the cutting edges 28 and 30 whereby thegrass is cut. The upturned vanes provided on end portions 20 and 22create additional turbulence for the grass cutting operation, as well asa flow pattern for discharging the cut grass upwardly and outwardly awayfrom the rotating blade. The ends of the blade forwardly of the notches32 and 34 reduce the strength of vortices created at the outer tip ofthe blade. Such weakened vortices, when colliding with weakened vorticesof adjacent blades of a multi-blade mower, produce less noise than knownblades not having vane notches. The notches reduce vane area and pumpingaction. However, the increased charge of air reaching the vane portionsof the blade as a result of the action of the downwardly sloped portions24 and 26 restores the pumping action.

What is claimed is:
 1. A rotary mower blade, comprising: an elongatedcentral portion joined at its opposite ends to respective intermediateportions which, in turn, are joined to respective end portions of theblade, said central, intermediate and end portions being disposed alonga common longitudinal blade axis; each of said end portions including asharpened edge surface extending towards the central portion along aleading edge of the blade, the sharpened edge of one of said endportions being disposed on the opposite side of the blade from the othersharpened edge; each of said end portions including an upwardlyprojecting vane located on a trailing edge of the blade; a notchprovided in an outside edge of each of said end portions adjacent arespective vane; and each of said intermediate portions being twistedequally in opposite senses at locations where the intermediate portionmeets the central portion and where it meets its respective end portionthereby forming an intermediate portion surface extending downwardlyfrom its associated leading edge towards its associated trailing edge.2. A blade according to claim 1, wherein each notch has an edgeextending from the trailing edge of the blade in a directionsubstantially perpendicular to the blade's longitudinal axis and then ina direction which is at an acute angle relative to the longitudinal axisof the blade.
 3. A blade according to claim 2, wherein said acute angleis approximately 30°.
 4. A blade according to claim 2, wherein the vanecomprises a bent segment of its respective end portion, the bendoccurring along a line substantially coextensive with the direction ofthe notch edge as it forms an acute angle relationship relative to thelongitudinal axis of the blade.
 5. A blade according to claim 4, whereinsaid acute angle is approximately 30°.
 6. A blade according to claim 1,wherein each intermediate portion is twisted by an amount which causesthe associated intermediate portion surface to extend downwardly at anangle of approximately 13° relative to the central portion.
 7. A bladeaccording to claim 6, wherein each notch has an edge extending from thetrailing edge of the blade in a direction substantially perpendicular tothe blade's longitudinal axis and then in a direction which is at anacute angle relative to the longitudinal axis of the blade.
 8. A bladeaccording to claim 7, wherein said acute angle is approximately 30°. 9.A blade according to claim 7, wherein the vane comprises a bent segmentof its respective end portion, the bend occurring along a linesubstantially coextensive with the direction of the notch edge as itforms an acute angle relationship relative to the longitudinal axis ofthe blade.
 10. A blade according to claim 9, wherein said acute angle isapproximately 30°.
 11. A blade according to claim 2, wherein the edge ofthe notch which is substantially perpendicular to the blade'slongitudinal axis extends a distance which is approximately half of theblade's width.